So you have a rooftop and you want to plant it but you are worried about the size and weight of the planters.
That’s a good concern to have ! The planter itself might not be crazy heavy – however once you put soil and a plant, or plants in it and then add water (soil weighs a lot more once wet ) it is very heavy.
Plant Specialists uses a light weight organic potting soil that is made up of Vermiculite ( an effective growing medium ), organic compost, loam or topsoil and a mix of decayed, bark, peat moss or coconut fiber.
Remember when you used to pot plants with your grandmother and you would look for a handful of rocks that you would throw into the bottom of the plants new home and that would be for drainage.
Grandma was right – you need to give the plants room to drain!
We don’t use rocks as they are heavy and super hard to find on a rooftop in Manhattan ! We use Styrofoam chips – now don’t get all excited and use any old chip that comes in your copious amount of Amazon packages. The chips need to be sealed and not absorb water or they compact over time and block the drainage holes of the planter that you are trying not to block !
We buy our chips from a company that produces them as off cuts when using a laser cutting machine – and they are waterproof.
The first thing you do to your planter is find some J drain and put it over the planters drainage holes ( on the inside of the planter – won’t do you much good on the outside !! ) It needs to be securely in place – either tape it or if possible staple it in place.
On top of the J drain we put a layer of peanuts – you can fill it as high or as low as you like, the more peanuts the lighter the planter. If you are planting a tree in the planter you are going to need to leave more space for the root ball of the tree. Annuals and Perennials will need less soil – so you can use more peanuts ( the planter should be proportionate as well – think 1/3 planter 2/3 tree or plant )
Do you have your J drain in place held to the inside bottom of the planter with Staples or tape, you have added your peanuts ( waterproof chips only ) you then add soil – no not yet hold your horses !
You then cover this layer with a layer of filter fabric – cut about one inch bigger on all sides of the planter. You put the filter cloth into the planter on top of the peanuts ( waterproof ) which is sitting on top of the J drain which is firmly attached to the inside bottom of the planter. When it is all in you run the extra inch of filter fabric up the sides of the planter – do not fopld it down or tuck it in. The reason it goes up is that it forms a cradle and will hold the soil in – if it goes down it will; allow the soil into the peanuts.
You can then add your lightweight potting mix, add a little at a time – make sure that you have a good amount of soil under the root ball of the plant you are putting into the planter. push the soil up on to all sides of the planter.
Add plants press down well – step back and look as what you think is straight when you are up close to it might be vastly different when you step back!
Soil should be below the rim of the planter or it will wash off and cause a huge mess or even a problem with your drains!
Water it in – the soil will compress with Water – then add more soil – no roots should be exposed !